Sealing ring and method of making same



y 30, 1957 J. H. RENTSCHLER 3,322,433

EALING R NG AND METHOD O MAKTNG 3AM Filed March 10, 1964 INVENTOR. Esm's'cwzz'z Jamv H.

ATTOPA/EKP v United States Patent 3,322,433 SEALING RING AND METHOD OF MAKING SAME John H. Rentschler, Minneapolis, Minn, assignor to Minnesota Rubber Company, Minneapolis, Minn., a corporation of Minnesota Filed Mar. 10, 1964, Ser. No. 350,747 2 Claims. (Cl. 277-228) The present invention is directed to a composite sealing ring, such as an O-ring structure, and the method of making same. More particularly, it is directed to a sealing ring formed of a solid elastomer having as a bonded coating therefor, a plurality of thin separately cured laminations of polyurethane upon the working face thereof. Even more specically, it relates in its more limited form to a sealing ring having a bonded coating on its working face comprised of a plurality of separately cured laminations of a mixture of polyurethane and a friction reducing filler composition.

Sealing rings, and particularly O-rings, have been utilized for sealing purposes for many years and have been formed of a wide variety of materials. These include rubbers, both natural and syntheticincluding polyurethanes-and also from non-elastomeric materials such as polytetrafluoroethylene. Each of these possesses some particular quality that makes its use desirable, but each also possesses limitations that lessens its field of application. Natural rubbers and most synthetic rubbers have the necessary flexibility to permit low pressure sealing when used as O-n'ngs, but the wear qualities are inferior to elastomers such as polyurethane. Polyurethane elastomers have the desired wear characteristics, but are so nonresilient in character as to require relatively high pressure engagement to insure sealing. Polytetrofluoroethylene and related plastics such as polychlorotrilluoroethylene have excellent low friction characteristics and are chemically inert, but are both expensive and because of their nonresilient nature, require high pressure engagement to effect sealing.

I have found that it is possible to incorporate the desirable features of each of the aforementioned classes of materials within a single sealing ring without incorporating their disadvantages. This is done in accordance with my invention by forming a composite structure comprised of a core and a plurality of very thin laminations bonded to the working face thereof. The main body of the structure is a highly resilient solid elastomer; silicone rubbers and fluoro-elastomers are specifically excluded. Over the sealing or working surface of the base structure of the preferred embodiment of the invention there is bonded a plurality of separately cured very thin films of polyurethane having included therein, as a filler material, an antifriction material such as graphite or tetrafiuoroethylene. I have found that such a sealing ring seals equally as well as a ring made solely of the conventional materials from which the base structure is formed, that it at least doubles the wear-life of the ring, and that it has a substantially lower coefiicient of friction and hence is more desirable.

Consequently it is a general object of my invention to provide a novel and improved sealing ring as an article of manufacture which is simple and inexpensive to manufacture and functions in a highly improved manner.

A more specific object is to provide a novel and improved sealing ring as an article of manufacture which has approximately double wear-life and substantially reduced friction characteristics and can be manufactured simply, easily, and inexpensively.

Another important object is to provide a novel, simple, and inexpensive method of producing a new article of manufacture in the form of a sealing ring having substantially improved wear-life and anti-friction characteristics.

Another object is to provide a novel and improved article of manufacture in the form of a sealing ring comprised of a conventional solid elastomeric sealing ring, exclusive of silicone rubber, fluoro elastomers, and polyurethane, rubber having a Shore durometer test of less than 40 or higher than 90, with a plurality of separately cured very thin laminations of polyurethane bonded on its working or sealing face and having improved wearing qualities and reduced friction qualities.

Another object is to provide a novel, simple, inexpensive and improved method of producing a new article of manufacture in the form of a sealing ring whereby a sealing coating having greatly improved wearing qualities may be bonded to the working face of the ring more efiectively than heretofore known and whereby a friction reducing filler may be included in the coating without weakening the bond.

Another object is to provide a novel and improved article of manufacture in the form of a sealing ring which is simple, and inexpensive to produce and is characterized by a vulcanized solid elastomeric core with a plurality of very thin laminated coating bonded in a superior manner on its working face and having as a filler therein a compound having a very low co-efiicient of friction whereby the coating has significantly lower friction qualities.

These and other objects and advantages of this invention will more fully appear from the following description, made in connection with the accompanying drawings, wherein like reference characters refer to the same or similar parts throughout the several views, and in which:

FIG. 1 is a cross-sectional view of an O-ring embodying my invention with the individual laminations of the laminated sheath shown in exaggerated proportional dimensions relative to the solid elastomeric core to better illustrate its construction;

FIG. 2 is a cross-sectional view of an O-ring embodying my invention with only its working face coated with polyurethane and the individual laminations of the coating shown in exaggerated proportional dimensions relative to the solid elastomeric core to better illustrate its construction;

FIG. 3 is a cross-sectional view of a sealing ring of another cross-sectional configuration and embodying my invention with the individual laminations of the laminated sheath of polyurethane shown in exaggerated proportional dimensions relative to the solid elastomeric core to better illustrate its construction; and

FIG. 4 is a cross-sectional view of the same cross-sectional configuration as that shown in FIG. 3 and embodying my invention with only its working faces coated with polyurethane and the individual laminations of the coat- I ing shown in exaggerated proportional dimensions relative to the solid elastomeric core to better illustrate its construction.

The invention will be described with respect to the use of a nitrile or neoprene rubber base stock which are preferred for the core although it should be recognized that the invention is equally applicable to other solid elastomers such as the natural rubbers, butyl rubbers and ethylene and propylene rubbers, but excluding the previously noted silicone rubbers and fiuoro elastomers. In addition, most polyurethane rubber base stock (as noted hereinbefore) does not possess sufficient resiliency to function as a core for a'relatively low pressure seal and would accordingly not be suitable for use in employing my invention since it does not possess the desirable low pressure sealing capability, although the desirable low friction characteristics of the material would be present.

In practice, the rubber base stock is molded into the desired configuration and vulcanized to a finished state as is conventional in the manufacture of O-rings or similar sealing rings of different cross-sectional configuration.

The ring is then cleaned in a strong detergent and water solution to remove the mold release material from its surface and the surface is then chlorinated. The chlorination step is not mandatory although markedly improved adhesion results from its use. Chlorination is readily accomplished by immersing the ring for 3-5 minutes in a solution of sodium hypochlorite (1-5%) acidified with hydrochloric acid (pH 12).

To prepare the coating material, a polyurethane resin is formulated by reacting a diisocyanate with a polyol to form a resin having a molecular weight of from about 500 to 1500 between isocyanate terminated cross-linking sites. The preferred formulation is as follows:

Moles Polypropylene glycol (average molecular weight 100-- 1 1-3-butanedio1 1 Trimethylol propane 1 Toluene diisocyanate 6 The above mixture is then reacted to form a resin in the absence of water. These materials, when freshly mixed, react exothermically. For the first hour, upon mixing, I cool the mixture sutficiently so as to maintain its batch temperature below 90 F. At the end of one hour, I raise the batch temperature by heating to 175 F. and maintain this temperature for about seven hours. At this point the prepolymer is ready for application to the base rubber rings.

Following the reaction the product is dissolved in a suitable solvent such as 1:1 mixture of xylene and Cellosolve acetate and a quantity of finely powdered (325 mesh) anti-friction agent is blended into the solvent-resin mixture. Various anti-friction materials can be used including molybdenum disulphide, graphite, and highly fluorinated ethylene propylene, chlorotrifiuoroethylene, and the like. I have found that the use of polytetrafiuoroethylene in from 10 to 20 parts per hundred by volume produces a final product having the best all around properties of good wear, adherence, and low friction. Various amounts of the anti-friction filler may be used, dependent on the requirements of the final product. However, above 25% by volume of tetrafiuoroethylene in the solvent free mixture is considered undesirable because it will result in diminished cohesion of the final film. Higher concentrations--up to about 40 parts per hundredof graphite or molybdenum disulfide can be used. However, the friction reducing characteristics are not as great for these materials as they are for polytetrafiuoroethylene in equivalent amounts.

The method of applying the polyurethane or polyurethane-anti-friction composition determines the quantity of solvent necessary. Dip coating is permissible, although spray coating of the base rubber ring is preferred. For spray coating 1:1 solvent to resin is suitable although more solvent is preferable. It is imperative that the dissolved polyurethane be applied, as illustrated in FIGS. 1-2, in a sufficiently thin layer 5 to the working face 6 of the base rubber ring indicated generally as 7 so that upon drying and curing, the film or laminate of polyurethane for any particular application shall not exceed 3 mils. A preferred thickness of the film is 13 mils although a thickness as low as 0.5 mil will provide definite advantages over a non-coated ring. Thereafter it is permitted to dry and cure through reaction with the moisture of the air. I have found that this curing action of the very thin film specified produces a bond of unexpected strength which will prevent peeling of the coating while under severe strain. Moreover such a sealing ring has wearing qualities which approximate twice the wearing quality of such a ring without such a coating on the wearing face and it provides only approximately one-tenth (or less) as much friction when it is moved relative to the face of an element against which it bears and upon which the seal to be perfected.

Final curing of the laminate of the coated ring working face, following evaporation of the solvent, takes place 4. upon exposure to the air at ordinary humidities. This vulcanization takes place in the known way with evolution of carbon dioxide. The reaction can be accelerated by exposure to elevated humidity and/ or by use of accelerators such as amines.

When thicknesses of the polyurethane coating greater than 3 mils are desired, the coating must be applied and cured successively in multiple layers not exceeding 3 mils each. This has been illustrated in FIGS. 1-2 wherein the second layer or film, applied after lamination 5 has cured, has been identified by the numeral 9. In no event, howi ever, may the aggregate thickness of the laminations exceed 10 mils if adequate sealing qualities are to be maintained.

When films in excess of 3 mils are to be produced on the base rubber, separate laminations must be cured individually by exposure to the moist air before application of subsequent films. This is necessary to produce proper bonding of the first lamination to the base rubber and of subsequent laminations to each other and insures that the evolution of CO brought about during curing does not cause bubbles to appear in the final film.

I have also found that if my invention is practiced as described above, even without the inclusion of the anti-friction material as a filler, the resultant sealing ring with its laminations of polyurethane on its working face, has substantially improved wear qualities and reduced friction qualities, as compared to a conventional elastomer sealing ring, although these qualities are not improved to the same extent as when the filler is used as described.

The article of manufacture resulting from coating the base rubber stock in the manner as first described above has markedly improved wear resistance over that of uncoated articles. The friction characteristics are likewise reduced to approach that of pure polytetrafiuoroethylene.

A relatively wide range of composition is permissible in formulating the polyurethane resin coating material. Almost any polyfunctional hydroxyl compound when formulated with a polyisocyanate will serve as a resin to produce a coated rubber base product possessing the improved characteristics of the present invention when applied as herein described.

Polyethylene and polybutylene glycols or polyesters may be used as diols in place of polypropylene glycols. Other suitable diols include pentanediol, dihydroxy castor oil derivatives and neopentyl glycol. Trimethylol ethane, castor oil, hexanetriol, and polyoxy propylene adducts of either hexane triol or glycerine may be used as trifunctional cross linking molecules. Aliphatic diols and triols having a carbon chain of 8 atoms or below are satisfactory. Above this the reactivity and properties of the product are less desirable.

The diisocyanate compound should be an aromatic based compound rather than the less reactive aliphatics.

In the compounding of the formulation to be used in coating of the base rubber sealing ring, variations of the preferred formulation may be used. However, to achieve the benefits of the invention, the molecular weight of the of the prepolymer resin should be maintained within the 5001500 figure. Thus selection of the diisocyanate and reactive hydroxyl group compounds should be made with this goal in mind.

It will be noted that in FIGS. 3-4 I have illustrated an application of my invention to a base rubber stock of a different cross-sectional configuration. In FIG. 3 the coating or sheath is comprised of a pair of laminates 10 and 11 which envelop the solid elastomeric ring 12. In FIG. 4 the laminates 13 and 14 of the coating are applied to the sealing or working face 15 of the ring 16.

Wherever herein the term organic carbon chain solid elastomeric material or the equivalent thereof is used it is intended to include all natural and synthetic rubbers with the exception of those polyurethanes indicated hereinbefore as having insufficient resiliency to function similar to the other natural and synthetic rubbers and is intended to exclude the silicone rubbers and fluoro elastomers.

It should be noted that the sealing rings produced in accordance with my invention are designed primarily for use at relatively low pressure levels although they will function and provide their advantages up to pressures in the area of as much as 3000 psi.

This it can be seen that I have provided a novel method of forming a new and improved article of manufacture which can be produced very inexpensively and has substantially improved desirable wearing qualities and reduced friction characteristics. Moreover, the advantages of my invention are readily attainable, easily and safely handled, and relatively inexpensive.

It will, of course, be understood that various changes may be made in the form, details, arrangement and proportions of the parts without departing from the scope of this invention which consists of the matter shown and described herein and set forth in the appended claims.

What is claimed is:

1. A sealing ring constructed principally of vulcanized solid organic carbon chain elastomeric material and having at least one working face, and a homogeneous coating bonded directly to said working face and covering the same, said coating being comprised of a polyurethane resin having an anti-friction filler of less than 25% by volume therein and having a radial thickness of from 0.5 mil to mil, said coating being comprised of a plurality of cured laminations of said resin and filler each lamination of which is no greater than 3 mils in radial thickness.

to, said coating being comprised of a polyurethane resin having an anti-friction filler therein and having a radial thickness of from 0.5 mil to 10 mils and being comprised of one or more superimposed separately cured laminations of said polyurethane resin, each lamination of which has a radial thickness of less than 3 mils.

References Cited UNITED STATES PATENTS 2,717,023 9/1955 Hetherington 277228 X 2,859,061 11/1958 Reid 277228 2,868,575 1/1959 Hawxhurst 277228 2,906,552 9/ 1959 White 277227 X 3,127,196 3/1964 Fabian et al. 285-111 OTHER REFERENCES Rubber Age, N.Y., H. E. Hill, 1961 (pages 979-987), TS 1870.R6.

LAVERNE D. GEIGER, Primary Examiner. JEFFREY S. MEDNICK, Assistant Examiner. 

1. A SEALING RING CONSTRUCTED PRINCIPALLY OF VULCANIZED SOLID ORGANIC CARBON CHAIN ELASTOMERIC MATERIAL AND HAVING AT LEAST ONE WORKING FACE, AND A HOMOGENEOUS COATING BONDED DIRECTLY TO SAID WORKING FACE AND COVERING THE SAME, SAID COATING BEING COMPRISED OF A PLYURETHANE RESIN HAVING AN ANTI-FRICTION FILLER OF LESS THAN 25% BY VOLUME THEREIN AND HAVING A RADIAL THICKNESS OF FROM 0.5 MIL TO 10 MIL, SAID COATING BEING COMPRISED OF A PLURALITY OF CURED LAMINATIONS OF SAID RESIN AND FILLER EACH LAMINATION OF WHICH IS NO GREATER THAN 3 MILS IN RADIAL THICKNESS. 